1. Field of the Invention
The present invention relates to a method of selecting an access network in accordance with a service provided, a user preference, or an operator policy in a communications network where multiple access networks are available.
2. Description of the Related Art
3GPP (Third Generation Partnership Protocol) technical specifications TS 23.122 v6.5.0 (June 2005) define a method of performing location registration through selection of an optimum network from combinations of operators' networks and access networks by a user or terminal.
According to the specifications, however, communications are always performed through the network on which the location registration has been performed, irrespective of the type of a service that the user wishes to use (for example, voice communications, data reception, etc.). Therefore, there is a problem in that even if there is another optimum network for the service that the user (terminal) wishes to use and the location of the user allows the user to use the network, the user can only use the network on which the user has performed location registration.
Further, there is also a problem in that the availability of resources on the network side, an operator policy, and the type of a network selected by a correspondent, which should be determined at the start of the communications, are not taken into consideration in selecting a network because the network selection is performed at the time of location registration by the terminal alone.
As the same idea as described above, Patent Document 1 discloses a method of determining which access network to connect to in a location where multiple access means (W-CDMA and WLAN, etc.) are available. However, the method described in Patent Document 1 also shows that a terminal selects an optimum one from multiple access networks, thus having the same problems as the above-described technical specifications TS 23.122.
On the other hand, Patent Document 2 proposes a method of selecting an optimum access network based on the resource information of each of multiple access networks by a common radio resource manager in a network. However, this proposal has a problem in that while the resource conditions of the access networks and an operator preference are considered, the preference of a user or terminal or the result of selection of an access network by a correspondent is not considered.
Further, Patent Document 3 discloses a method of performing handover from an access network to another access network at a location where multiple access means (W-CDMA and WLAN, etc.) are available at the time of handover.
This method disclosed in Patent Document 3 shows that a terminal selects an optimum one from multiple access networks, and the location and moving speed of the terminal itself, cost, network QoS (Quality of Service) information, battery consumption, etc., are cited as information for the terminal selecting an access network. However, this method also has the same problem as described above in that the result of selection of an access network in the case of handover by a correspondent is not considered.
In 3GPP, TS 25.401 v6.6.0 (June 2005) defines handover within the access networks of the same type (within GERANs and within UTRANs) and between different access networks (between GERAN and UTRAN). Whether to perform this handover is determined by the access network based on the information of which the access network is notified by the terminal, such as the intensity of the radio wave received by the terminal. Accordingly, a core network does not intervene in this determination, so that there is a problem in that the QoS of the entire network, an operator policy, or the type of the access network used by a correspondent is not considered.    [Patent Document 1] Japanese Laid-Open Patent Application No. 2005-110262    [Patent Document 2] Japanese Translation of PCT International Application No. 2004-511988    [Patent Document 3] Japanese Laid-Open Patent Application No. 2003-333639
As described above, conventionally, the access network used to perform communications is fixed to the access network selected by a terminal or used at the time of location registration even if multiple access networks are available.
Further, in the case of selecting an optimum access network in accordance with the resource conditions of each access network, the access network is selected based only on the information detectable by the terminal (user) (such as the availability of the resources of a radio section). Therefore, a user preference such as which network the user wishes to use or the result of selection of an access network by a correspondent is not considered, so that there is a problem in that an optimum access network is not necessarily selected from the viewpoint of the entire communication-related path.